Dear Peter Sorry about joining this discussion late but I think this sounds familiar with an issue I had on a military training system I had a number years ago (2018) which was failing ITE Radiated Emissions limits by 6dB. The training system mainly consisted of COTS ITE together with some custom military kit. Our troubleshooting identified the emissions were coming from the HDMI cables connected to a COTS HDMI Splitter feeding COTS Monitors. We measured CM currents on these HDMI cables which we suppressed using clip on cable Ferrites but also found high emissions from the COTS HDMI Splitter which was CE Marked and its D of C stated it complied with ITE Radiated Emissions. While the system now 'just' met the radiated emissions limits and we were time limited to complete testing and ship the system we took the additional step to fit the COTS HDMI Splitter in a modified sealed Diecast Box which improved our test limit pass margin by over 6dB at the problem frequencies.
During this time I came across an article by EMC Expert Ken Wyatt entitled "HDMI cables and EMI" in Interference Technology online at HDMI Cables and EMI | Interference Technology<https://interferencetechnology.com/hdmi-cables-emi/>. This highlighted the differences in HDMI cable shielding should in 20dB differences in emissions performance due to limitations in the HDMI cable specification then. But I am not sure if the specification has been updated since 2017 to address this or not! Thought this article might be of interest. Regards Philip Stevenson ________________________________ From: James Pawson (U3C) <[email protected]> Sent: Sunday, May 18, 2025 20:06 To: [email protected] <[email protected]> Subject: Re: [PSES] HDMI cable emissions Hi Peter, In my experiments about 10 years ago I found that the quietest source from a signal CM noise perspective was a Sony Playstation 3. If I was looking today I’d probably start with something from Apple. Cable shielding is normally a second order affair when compared to termination of the shield and connector (in my experience) You can use an electric or magnetic near field probe around the connector backshells to detect field leakage. Ironically the worst was the Quantum Data video generator that we used for HDMI signal qualification. Best of luck. All the best James James Pawson Managing Director & EMC Problem Solver Unit 3 Compliance Ltd EMC : Environmental & Vibration : Electrical Safety : CE & UKCA : Consultancy www.unit3compliance.co.uk<http://www.unit3compliance.co.uk/> | [email protected]<mailto:[email protected]> +44(0)1274 911747 | +44(0)7811 139957 2 Wellington Business Park, New Lane, Bradford, BD4 8AL Registered in England and Wales # 10574298 For inquiries, bookings, and testing updates please send us an email on [email protected]<mailto:[email protected]> or call 01274 911747. Our lead times for testing and consultancy are typically 4-5 weeks. From: [email protected] <[email protected]> Sent: 18 May 2025 19:57 To: [email protected] Subject: Re: [PSES] HDMI cable emissions Thank you all for your valuable feedback. It is greatly appreciated. Individual pair are shileded using foil and the braid coverage is more than 75%. The main problem frequency is 741 which is the harmonic of the main clock frequency. The PCB layout seems good. I am fairly sure the issue is related to source and sink. When I test the cable at a 3rd party lab, 741MHz is very low but they see issue at higher frequency. If I can find a quiet source, I think I am going to solve this. I am digging further. Thank you again Peter On Friday, May 16, 2025 at 03:30:23 AM PDT, Charlie Blackham <[email protected]<mailto:[email protected]>> wrote: Just to add to this discussion, I’ve found that bought cables have a wide variety of end-connector to end-connector resistances – anywhere between 4-100M ohm down to 30-50 milli ohm. Assuming the cable is 1-2 m long, 30-50 milliohm cable impedance would rule the cable out from being the problem. Measure resistance using a 4-port meter, which can be bought quite cheaply and this one works well, https://www.amazon.co.uk/Milliohm-Milli-ohm-Resistance-Multimeter-Accuracy/dp/B08WTQRCF5 Best regards Charlie Charlie Blackham Sulis Consultants Limited Tel: +44 (0)7946 624317 Web: https://sulisconsultants.com/ Registered in England and Wales, number 05466247 From: James Pawson (U3C) <[email protected]<mailto:[email protected]>> Sent: 16 May 2025 09:25 To: [email protected]<mailto:[email protected]> Subject: Re: [PSES] HDMI cable emissions Hi Peter, Cable quality is important, mostly in terms of terminating the shield well to the connector backshell. Good quality off the shelf cables are hard to find, particularly from low cost online re-sellers. We went through many samples of trial and error before we found some that worked well. What is the source of the noise? Mostly imbalance in the differential signal. Uneven rise/fall times, unequal duty cycles within the pairs, amplitude differences, impedance differences on lines… it all accrues to give pulses of common mode current mostly aligned with the rising / falling edges of the signals. You’ll see harmonics of the clock signal, I remember 741.16MHz being particularly troublesome. Frequencies will change significantly with mode (480i/576i, 720p, 1080i, 1080p) and slightly with frame rate (50/60Hz) Fixing the imbalance can be very difficult. In many cases it is baked in to the driver silicon and there is not much that can be done. Ted Eckert’s comment about PCB layout is worth taking note of. The quality of the sink and how it handles the return of the CM currents is also key. Try removing the sink from the test chamber via a long cable or wrapping it in tinfoil and terminating the shield to the cable shield. I did make a proper self powered TMDS + EDID termination for EMC testing of HDMI signals and it still does occasional duty in our lab. It pretended to be a 4k Samsung 5” TV but in reality only had one pixel – the little light to tell you it was on. I really should redesign it and make them more widely available. Connecting cable screen with a low impedance (not just resistance) bond from connector shell to metal chassis if available (ref Karen B’s comment) can be very useful. Since this isn’t always available, making sure there is a low impedance connection from connector shell to PCB 0V plane should also be implemented regardless of chassis connection. Try other sources and sinks, try lots of cables, try connection of cable shields to PCB and chassis, if you have high speed scopes try quantifying the signal imbalance and CM component (difficult), try ferrite cores (YMMV), go over your layout with a fine tooth comb. Best of luck, I spent years working on exactly this problem. With careful layout and cable selection I have achieved a Class B emissions pass at 1080p/60 with a single 4 layer PCB in a plastic chassis with a 3dB margin. All the best James James Pawson Managing Director & EMC Problem Solver Unit 3 Compliance Ltd EMC : Environmental & Vibration : Electrical Safety : CE & UKCA : Consultancy www.unit3compliance.co.uk<http://www.unit3compliance.co.uk/> | [email protected]<mailto:[email protected]> +44(0)1274 911747 | +44(0)7811 139957 2 Wellington Business Park, New Lane, Bradford, BD4 8AL Registered in England and Wales # 10574298 For inquiries, bookings, and testing updates please send us an email on [email protected]<mailto:[email protected]> or call 01274 911747. Our lead times for testing and consultancy are typically 4-5 weeks. From: [email protected]<mailto:[email protected]> <[email protected]<mailto:[email protected]>> Sent: 15 May 2025 16:44 To: [email protected]<mailto:[email protected]> Subject: [PSES] HDMI cable emissions Hello group, I am working on a HDMI cable where it does not pass radiated emissions with good margin. I have great braid coverage and have soldered the braid to the connector shell and have fully sealed and covered it with copper tape. Is there anything else that I need to do? My issue is mainly at below GHz when I use 1080P resolution. Thank you Peter ________________________________ This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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